Reaction Of NO Research Articles

Quantitative analyses of NO formations from different reaction pathways in methane-air combustion at various pressures and temperatures

Numerical calculations of the laminar counterflow diffusion flames of methane-air are conducted to quantitatively study NO formations from different reaction pathways (mechanisms) at various pressures and/or initial air temperatures. A modified method, which deactivates the initiating reactions in a specific reaction pathway only for NO production while maintaining interactions with other pathways, is developed to calculate NO formation in each mechanism. Results indicate that in the thermal, prompt, N2O, and NNH reaction mechanisms, the NO production rate largely increases as the pressure or the initial air temperature increases, and in particular, as these two parameters are increased together as in a practical combustion system. In the thermal pathway, as the pressure is increased to 15 atm, NO is produced almost entirely on the fuel-lean side. In the prompt pathway, NO production generally occurs in regions with the progress variable ranging from 0.8 to 0.95; the maximum NO production rate moves from the fuel-rich towards the stoichiometric region as the pressure is increased. NO formation from the N2O or NNH mechanism occurs mainly at high pressures, but the corresponding production rate is an order of magnitude smaller than that from the thermal or prompt mechanism, respectively. In all the reaction mechanisms, NO consumption occurs through the reburn mechanism on the fuel-rich side, and the consumption rate significantly increases as the pressure and initial air temperature increase. Results herein provide a quantitative understanding of the effects of pressure and temperature on NO formations from different reaction mechanisms.

Mesoporous PdN Alloy Nanocubes for Efficient Electrochemical Nitrate Reduction to Ammonia.

Developing highly active and selective electrocatalysts for electrochemical nitrate reduction reaction (NITRR) is very important for synthesizing recyclable ammonia (NH3 ) in an economic and environmentally friendly manner. Despite some encouraging progress, their activity and selectivity have been remarkably slower than expected. In this manuscript, mesoporous palladium-nonmetal (meso-PdX) nanocubes (NCs) are reported as a new series of highly efficient electrocatalysts for selective nitrate reduction reaction (NITRR) electrocatalysis to NH3 . The samples feature uniformly alloyed compositions and highly penetrated mesopores with abundant highly active sites and optimized electronic structures. The best meso-PdN NCs hold an outstanding NITRR activity and selectivity with a remarkable NH3 Faradaic efficiency of 96.1% and a yield rate of 3760µg h-1 mg-1 , suppressing the state-of-the-art electrocatalysts. Meanwhile, meso-PdN NCs are electrocatalytically stable, retaining well the activity and selectivity of NO3 - -to-NH3 electrocatalysis for more than 20 cycles. Detailed mechanism studies ascribe the superior performance to combined compositional and structural synergies of meso-PdN NCs that not only promote the adsorption (reactivity) of NO3 - and the desorption of NH3 but also increase the retention time of key intermediates for the deeper NITRR electrocatalysis to NH3 through an eight-electron pathway.

Atmospheric chemistry of nitrous acid and its effects on hydroxyl radical and ozone at the urban area of Beijing in early spring 2021

The atmospheric chemistry of nitrous acid (HONO) has received extensive attention because of its significant contribution to hydroxyl (OH) radicals. Heterogeneous reaction of NO2 is an important HONO source, and its reaction mechanism is affected by many factors, such as concentration of gaseous NO2, surface adsorbed water, relative humidity and temperature. Although laboratory studies have confirmed the effect of temperature on heterogeneous reaction of NO2, there are few field observations reporting about it. We have conducted a field observation in the early spring 2021 when the temperature ranges widely (−0.1–24.7 °C). Concentrations of HONO and related pollutants at the urban area of Beijing are obtained. The hourly averaged HONO concentration reaches 4.87 ppb with a mean value of 1.48 ± 1.09 ppb. Combined with box model and RACM2 mechanism, we found an optimal temperature (∼10 °C) existing for heterogeneous reaction of NO2 during this measurement. When considering the promotion effect of optimal temperature, the contribution of heterogeneous reaction of NO2 to HONO can increase by 10%. This result will provide essential information for developing an accurate model of HONO chemistry in the atmosphere especially for certain periods or regions with temperature changing largely. Moreover, heterogeneous reaction of NO2 is the vital source of HONO, contributing 63–76% to simulated HONO during this measurement. Note that HONO photolysis is the most important formation pathway of OH radicals, and ambient HONO concentration is the obbligato constraint for evaluating atmospheric oxidation by model simulations.

Effect of NO2 addition on flame dynamics and chemical kinetics of near-limit n-dodecane cool and warm diffusion flames

The present study is a continuation of the previous study by Zhou et al. (2021), in which kinetic effects of NO addition on n-dodecane cool and warm diffusion flames are investigated via counterflow flames and a skeletal n-dodecane/NOx model is developed by performing jet-stirred reactor experiments. Here, effects of NO2 addition on the flame dynamics and kinetics of n-dodecane diffusion flames are studied. The focus is on understanding the kinetic effects of NO2 on cool flame extinction limits and the transitions between cool, warm, and hot flames and elucidating the differentiated effects of NO and NO2 on low- and intermediate-temperature chemistry of n-dodecane. NO2 also plays different roles in cool and warm flames. Specifically, NO2 addition reduces the cool flame temperature and strain rates at cool flame extinction, indicating that NO2 inhibits the low-temperature chemistry of n-dodecane. NO2 addition increases the warm flame temperature, delays the warm flames extinction to cool flames, and promotes the warm flames re-ignition to hot flames, demonstrating NO2 enhances the intermediate-temperature oxidation of n-dodecane. However, reaction pathways and sensitivity analyses reveal that reactions responsible for NO2 and NO affecting the low- and intermediate-temperature oxidation of n-dodecane diffusion flames are differentiated. For cool flames, reaction R + NO2 <=> RO + NO for NO2 addition and reaction RO2 + NO <=> RO + NO2 for NO addition are the major corresponding reactions, respectively, which compete with the low-temperature chain-branching reaction pathway. For warm flames, the kinetic effects of NO on the intermediate-temperature oxidation are due to NO converting the relative inactive HO2 to reactive OH radicals via the reaction NO + HO2 <=> OH + NO2, which simultaneously accelerates radical production of QOOH => QO + OH to the increase of warm flame temperature, while the effect of NO2 is mainly induced by the conservation of NO2 to NO. Moreover, comparisons of the effects of NO and NO2 addition on cool flame extinction limits are performed, and results show that the kinetic effects of NO2 addition are weaker than those of NO addition since the effects of NO2 are partially contributed by NO from the conservation of NO2.

Comparing the Reactivities of Methanol and Methanediol in the Photolysis of Aqueous Nitrite Solution.

Ultraviolet irradiation of aqueous nitrite (NO2-) quickly generates hydroxyl (OH) and nitric oxide (NO) radicals, which are subsequently consumed concomitantly with the generation of NxOy species. Recently, dissolved formaldehyde (CH2O) in aqueous solution (e.g., methanediol, CH2(OH)2), has been regarded as the precursor in the formation of atmospheric formic acid (HCOOH) via the reaction with OH and cascading processes ( Nature2021, 593, 233-237). In this work, a step-scan Fourier transform interferometer was utilized to monitor the time-resolved difference infrared spectra of NaNO2 aqueous solution in the presences of methanediol and methanol upon pulsed irradiation at 355 nm. The fates of the dinitrogen trioxide (N2O3), generated via a series of reactions of OH, NO, and NO2-, differed in the presences of CH2(OH)2 and CH3OH. The decay of N2O3 via hydrolysis with H2O was retarded more by CH3OH than by CH2(OH)2. The monohydroxyl group of CH3OH does not behave like the hydroxyl group of water, whereas the two hydroxyl groups of CH2(OH)2 can be treated as a water reservoir via the quick equilibrium between H2O and CH2O, further facilitating the hydrolytic solvation reaction of N2O3. The observed difference in reaction kinetics involving hydration should be thoroughly taken into consideration in formaldehyde-related aqueous reactions.

Oxidation of Catechols at the Air-Water Interface by Nitrate Radicals.

Abundant substituted catechols are emitted to, and created in, the atmosphere during wildfires and anthropogenic combustion and agro-industrial processes. While ozone (O3) and hydroxyl radicals (HO•) efficiently react in a 1 μs contact time with catechols at the air-water interface, the nighttime reactivity dominated by nitrate radicals (NO3) remains unexplored. Herein, online electrospray ionization mass spectrometry (OESI-MS) is used to explore the reaction of NO3(g) with a series of representative catechols (catechol, pyrogallol, 3-methylcatechol, 4-methylcatechol, and 3-methoxycatechol) on the surface of aqueous microdroplets. The work detects the ultrafast generation of nitrocatechol (aromatic) compounds, which are major constituents of atmospheric brown carbon. Two mechanisms are proposed to produce nitrocatechols, one (equivalent to H atom abstraction) following fast electron transfer from the catechols (QH2) to NO3, forming NO3- and QH2•+ that quickly deprotonates into a semiquinone radical (QH•). The second mechanism proceeds via cyclohexadienyl radical intermediates from NO3 attack to the ring. Experiments in the pH range from 4 to 8 showed that the production of nitrocatechols was favored under the most acidic conditions. Mechanistically, the results explain the interfacial production of chromophoric nitrocatechols that modify the absorption properties of tropospheric particles, making them more susceptible to photooxidation, and alter the Earth's radiative forcing.

Theoretical study of the mechanism and kinetics of the atmospheric reaction of acrylic acid with NO3 radical

AbstractThe nitrate radical is one of the most significant oxidants in troposphere at the nighttime. Furthermore, acrylic acid is reported to be one of 189 hazardous air pollutants. In order to investigate the atmospheric chemistry and environmental impact of acrylic acid with nitrate radical, in this work, the atmospheric reaction mechanisms of acrylic acid by NO3 radical have been discussed by the CCSD(T)/cc‐pVTZ//M06‐2X/6‐311++G(d, p) dual‐level of theory at the first time. The energy barriers of NO3 and CH2CHCOOH reaction have also been calculated accurately. The additions between NO3 with CH2CHCOOH would produce the dominant intermediates CH2NO3CHCOOH and CH2CHNO3COOH via low barriers. All hydrogen abstraction channels have higher barriers than that of additions. Therefore, addition pathways play an important role in this reaction. The total and branching rate constants have been computed by conventional transition state theory via the Variflex code. These rate constants of NO3 and acrylic acid reaction would be useful to complete structure–activity relationships of reaction rate. The calculated atmospheric lifetime of acrylic acid by NO3 is about 3.66 days at night. All findings will help us gain a better understanding of atmospheric chemistry of acrylic acid.

Seasonal variation in nitryl chloride and its relation to gas-phase precursors during the JULIAC campaign in Germany

Abstract. Ambient measurements of nitryl chloride (ClNO2) were performed at a rural site in Germany, covering three periods in winter, summer, and autumn 2019, as part of the JULIAC campaign (Jülich Atmospheric Chemistry Project) that aimed to understand the photochemical processes in air masses typical of midwestern Europe. Measurements were conducted at 50 m aboveground, which was mainly located in the nocturnal boundary layer and thus uncoupled from local surface emissions. ClNO2 is produced at night by the heterogeneous reaction of dinitrogen pentoxide (N2O5) on chloride (Cl−) that contains aerosol. Its photolysis during the day is of general interest, as it produces chlorine (Cl) atoms that react with different atmospheric trace gases to form radicals. The highest-observed ClNO2 mixing ratio was 1.6 ppbv (parts per billion by volume; 15 min average) during the night of 20 September. Air masses reaching the measurement site either originated from long-range transport from the southwest and had an oceanic influence or circulated in the nearby region and were influenced by anthropogenic activities. Nocturnal maximum ClNO2 mixing ratios were around 0.2 ppbv if originating from long-range transport in nearly all seasons, while the values were higher, ranging from 0.4 to 0.6 ppbv for regionally influenced air. The chemical composition of long-range transported air was similar in all investigated seasons, while the regional air exhibited larger differences between the seasons. The N2O5 necessary for ClNO2 formation comes from the reaction of nitrate radicals (NO3) with nitrogen dioxide (NO2), where NO3 itself is formed by a reaction of NO2 with ozone (O3). Measured concentrations of ClNO2, NO2, and O3 were used to quantify ClNO2 production efficiencies, i.e., the yield of ClNO2 formation per NO3 radical formed, and a box model was used to examine the idealized dependence of ClNO2 on the observed nocturnal O3 and NO2 concentrations. Results indicate that ClNO2 production efficiency was most sensitive to the availability of NO2 rather than that of O3 and increased with decreasing temperature. The average ClNO2 production efficiency was highest in February and September, with values of 18 %, and was lowest in December, with values of 3 %. The average ClNO2 production efficiencies were in the range of 3 % and 6 % from August to November for air masses originating from long-range transportation. These numbers are at the high end of values reported in the literature, indicating the importance of ClNO2 chemistry in rural environments in midwestern Europe.

Effects of NOX and O2 on the Reaction of Ca(OH)2 with CO2 at Low Temperatures

The effects of NOX and O2 on the reaction of Ca(OH)2 with CO2 were studied under low-temperature and humid conditions prevailing in dry or semidry flue gas desulfurization processes. Without the simultaneous presence of NOX and O2, the extent of the carbonation of Ca(OH)2 was low and not affected by the concentration of CO2, NOX, or O2. With the simultaneous presence of NOX and O2, the carbonation of Ca(OH)2 was greatly enhanced, and the CO2 capture increased by more than 2 times at a relative humidity higher than 40%; in addition, the relative humidity and NOX concentration had positive effects, the temperature and O2 concentration had negligible effects, but the CO2 concentration had a negative effect. The simultaneous presence of NOX and O2 enhanced the formation of nitric and nitrous acids and salts of calcium nitrate and nitrite. The deliquescence of these salts collected a great quantity of water and thus enhanced the reactions of Ca(OH)2 with the reactive gases. Ca(OH)2 could be completely converted when reacted with the mixture of CO2, NOX, and O2 at a relative humidity ≥ 50% and a NOX concentration ≥ 300 ppm; CaCO3 formed would further react with NOX and O2 to form Ca(NO3)2 when Ca(OH)2 was depleted. The highest CO2 capture obtained was 0.49 g of CO2/g of sorbent (reacted at 60 °C, 70% relative humidity (RH), 12.6% CO2, 2400 ppm NOX, and 5% O2 for 1 h). The major products for the reactions of NO2 with Ca(OH)2 and CaCO3 were calcium nitrite and nitrate, respectively. The capture of CO2 in practice is preferably carried out before removing NOX and after removing SO2 from the flue gas. This work is useful to the development of technologies for CO2 capture using solid wastes containing CaO/Ca(OH)2.

(Invited) Synthesis of Dinitrogen Pentoxide Using Air Atmospheric Pressure Plasmas and Application for Biomaterial Processes

Atmospheric-pressure plasma (APP) technology, enabling to convert air molecules into multi-functional reactive species [e.g., reactive oxygen and nitrogen species (RONS)] with electricity, has been of great interest and extensively investigated. In particular, air APP devices, working only with air and electricity, can potentially allow for ubiquitous supply of RONS, which can be applied in a wide range of fields such as medical, agricultural, environmental, and biomaterial fields [1-4]. Recently, we have developed a new composite air APP device consisting low temperature and high temperature plasma reactors, enabling to supply RONS [e.g., dinitrogen pentoxide (N2O5), ozone (O3), nitric oxides (NOx), ...] with fine control and good reproducibility [5]. Specifically, its ability to generate high density (up to 200 ppm) N2O5 with high selectivity is quite unique and could accelerate scientific and industrial N2O5 applications. In addition, the APP device can utilize room air and renewable energy sources, such as a solar cell, and thus can realize sustainable and ubiquitous N2O5 supply.N2O5 is well known as a powerful oxidizing and nitrating agent and can potentially be bioactive. However, there are no previous studies using N2O5 in bio-applications, to our best knowledge. The reason is possibly due to its ordinary synthesis methods requiring multiple hazardous raw materials (requiring handling with much care). The air APP devices is user-friendly and can easily supply N2O5 to biomaterials (e.g., amino acid, protein, cells, virus, bacteria, ...). Thus, we are exploring the inactivation effects of N2O5 exposure on pathogen and virus, and modification of amino acid by the plasma-synthesized N2O5.Using the air APP device, we have investigated the inactivation effects on C. glo eosporioides (strawberry pathogen) and Qβ phage (RNA virus). 10μL of water droplet containing C. gloeosporioides was exposed to the plasma-synthesized N2O5 gas for 60 s, and typically 8h later, the germination rate of C. gloeosporioides conidium was evaluated as an indicator of inactivation effects. As a result, the N2O5 exposure significantly decreased the germination rate and the inactivation effect was not only due to pH decrease by HNO3aq transfer into the droplet from N2O5 gas. This indicates that N2O5aq, [NO2 +][ NO3 -]aq, or NO2 + aq may contribute to the inactivation. Also, mist particles containing Qβ phage were exposed to the plasma-synthesized N2O5gas, and the N2O5gas treatment resulted in over 3-log reduction in titer of Qβ phage. In addition, there were no significant difference of the inactivation effect between water and phosphate buffer mists, suggesting unique inactivation effects of N2O5gas other than pH decrease as noted above.Furthermore, we conducted experiments on the modification of amino acids such as tyrosine by plasma-synthesized N2O5gas. Tyrosine solution was treated by N2O5gas together with several reactive species such as O3gas or NO2gas, and it is found that dopachrome and nitrotyrosine were generated by the modification of tyrosine. Interestingly, dopachrome generation rate in N2O5gas with excess O3gas was most high, and the dopachrome generation was correlated with O3gas density. Further analysis using LC-PDA (liquid chromatography-photodiode array) and MS (mass spectrometer) quantified the tyrosine and tyrosine derivatives, and tyrosine was consumed at high rate, especially under N2O5gas with O3gas treatment.Major role of NO2 + aq is considered to be strong oxidizing capacity like OH radical, and N2O5gas triggers the generation of tyrosine intermediates. The tyrosine intermediates rapidly react with other reactive species such as O3gas and NO2gas, and then, dopachrome was significantly generated in N2O5gas with O3gas treatment and nitrotyrosine was in N2O5gas with NO2gas treatment.In the presentation, the details of the various biomaterial APP processes and plasma-synthesized N2O5 reaction pathway in the gas and liquid phase will be discussed.[1] Y. Kimura, K. Takashima, S. Sasaki, and T. Kaneko: J. Phys. D. Appl. Phys. 52, 064003 (2019).[2] K. Shimada, K. Takashima, Y. Kimura, K. Nihei, H. Konishi, and T. Kaneko: Plasma Process. Polym. 17, e1900004 (2020).[3] K. Takashima, Y. Hu, T. Goto, S. Sasaki, and T. Kaneko: J. Phys. D. Appl. Phys. 53, 354004 (2020).[4] K. Takashima, A.S. bin Ahmad Nor, S. Ando, H. Takahashi, and T. Kaneko: Jpn. J. Appl. Phys. 60, 010504 (2020).[5] S. Sasaki, K. Takashima, and T. Kaneko: Ind. Eng. Chem. Res. 60, 798 (2021).

A Miniaturized Electrochemical Nitrate Sensor and the Design for Its Automatic Operation Based on Distributed Model

As one of the most common inorganic ions in daily food and ecological environment, nitrate (NO3−) is potentially harmful to both environment and humans. Therefore, the detection of nitrate concentration is quite important. Chemical sensors, as analytical measurement tools, usually demonstrate high selectivity, fast analysis speed, simple structure, convenient operation, and low cost and are considered to be a promising method for ion identification and detection. In this paper, a miniaturized electrochemical electrode is fabricated based on the microfabrication technology, and an electrochemical sensor for the detection of nitrate concentration in water is developed by combining the deposition technology of nanometal particles with electrochemical analysis technique. The developed electrochemical sensor utilizes electrochemical deposition to prepare a copper (Cu) granular sensitive film with a branch-cluster structure on the surface of a circular working electrode (Pt). Using copper’s characteristics of electrocatalytic reduction of NO3− in the acid solution environment (pH = 2), the concentration of NO3− in the water sample was calculated by measuring the reduction current on the working electrode when the electrocatalytic reduction reaction of NO3− occurred on the surface of the copper-sensitive membrane. The sensitive film is characterized and detected both with the scanning electron microscope (SEM) and X-ray diffraction analysis (XRD) technique; and the microsensor is used to detect nitrate standard samples; a high detection sensitivity (24.9 μA/mmol·L−1) is achieved in the concentration range of 0.0 to 3.0 mmol/L. At the same time, a MEMS three-electrode sensor without gold wire bonding and insulating glue packaging is designed, and an automatic detection system is constructed with a STM32f103 microcontroller as the controller to realize the automated detecting process for nitrate ions. At the same time, a distributed system is constructed, which can describe the nitrate concentration in every position of the water area and realize the monitoring of the whole water area. The detection system can meet the working environment under most conditions and has practical significance.

Density functional theory study on catalytic reduction of NO on semi-coke containing N and Fe: The effect of CO

NOx is a common air pollutant, and its removal research is imminent. In this paper, the semi-coke segment was used as the catalyst carrier to study the three important factors of nitrogen doping, iron doping and CO introduction, and the NO heterogeneous reduction was analyzed by the DFT calculation method. And at the range of 300 to 1000 K, the reaction kinetics was quantitatively analyzed by the conventional transition state theory (TST). Only one NO molecule was needed to finish the whole reaction path by doping the nitrogen, as suggested the nitrogen doping improved the NO removal rate at low NO concentrations. Through the analysis of the adsorption energy, it was found that the adsorption capacity of carbon active sites for NO and CO was significantly enhanced with iron doping. Among them, the appearance of FeO groups also reduced the activation energy of the stage reaction. In addition, the CO introduction significantly promoted the production of N2, CO2 and N2O, which was manifested in the reduction of activation energy of NO catalytic reaction and the increase of the N2 and N2O reaction rate constant. This theoretical research provided a theoretical foundation for the subsequent experimental research on NO removal.

Identification of highly oxygenated organic molecules and their role in aerosol formation in the reaction of limonene with nitrate radical

Abstract. Nighttime NO3-initiated oxidation of biogenic volatile organic compounds (BVOCs) such as monoterpenes is important for the atmospheric formation and growth of secondary organic aerosol (SOA), which has significant impact on climate, air quality, and human health. In such SOA formation and growth, highly oxygenated organic molecules (HOM) may be crucial, but their formation pathways and role in aerosol formation have yet to be clarified. Among monoterpenes, limonene is of particular interest for its high emission globally and high SOA yield. In this work, HOM formation in the reaction of limonene with nitrate radical (NO3) was investigated in the SAPHIR chamber (Simulation of Atmospheric PHotochemistry In a large Reaction chamber). About 280 HOM products were identified, grouped into 19 monomer families, 11 dimer families, and 3 trimer families. Both closed-shell products and open-shell peroxy radicals (RO2⚫) were observed, and many of them have not been reported previously. Monomers and dimers accounted for 47 % and 47 % of HOM concentrations, respectively, with trimers making up the remaining 6 %. In the most abundant monomer families, C10H15−17NO6−14, carbonyl products outnumbered hydroxyl products, indicating the importance of RO2⚫ termination by unimolecular dissociation. Both RO2⚫ autoxidation and alkoxy–peroxy pathways were found to be important processes leading to HOM. Time-dependent concentration profiles of monomer products containing nitrogen showed mainly second-generation formation patterns. Dimers were likely formed via the accretion reaction of two monomer RO2⚫, and HOM-trimers via the accretion reaction between monomer RO2⚫ and dimer RO2⚫. Trimers are suggested to play an important role in new particle formation (NPF) observed in our experiment. A HOM yield of 1.5%-0.7%+1.7% was estimated considering only first-generation products. SOA mass growth could be reasonably explained by HOM condensation on particles assuming irreversible uptake of ultra-low volatility organic compounds (ULVOCs), extremely low volatility organic compounds (ELVOCs), and low volatility organic compounds (LVOCs). This work provides evidence for the important role of HOM formed via the limonene +NO3 reaction in NPF and growth of SOA particles.

The effect of the addition of nitrogen oxides on the oxidation of propane: An experimental and modeling study

The oxidation of propane (C3H8), with the addition of different oxides of nitrogen (NO, NO2, and N2O) in concentrations of 0 – 2000 ppm, has been investigated for stoichiometric mixtures, at compressed temperatures of (TC) = 690 – 1420 K, and at compressed pressures of (pC) = 2.0 – 3.0 MPa using both a rapid compression machine and a high-pressure shock tube. These new ignition delay time (IDT) measurements, together with C3/NOx data available in the literature, provide a direct validation of NUIGMech1.3 which includes an updated C3/NOx sub-mechanism. The experimental results show that the mixtures with NO2 and NO/NO2 added have longer IDTs, inhibiting reactivity at TC〈 800 K, and shorter IDTs, promoting reactivity at TC〉 800 K, compared to the base C3H8/‘air’ mixtures indicating the complex chemical interactions involved. Both the inhibiting and prompting effects depend on the concentrations of NO and NO2 added and on the temperature regime. The addition of 1000 ppm NO2 significantly reduces the negative temperature coefficient (NTC) behavior of C3H8 in the temperature range 715–800 K compared to the addition of 200 ppm. Model predictions with 1000 ppm NO added, assuming no conversion of NO to NO2, are significantly slower than for both the 0 and 1000 ppm NO2 addition cases at TC < 800 K. Although NO and NO2 addition have different impacts on C3H8 oxidation at low-, intermediate, and high-temperatures, the addition of 1000 ppm N2O did not show any chemical effect at the conditions studied. NUIGMech1.3, with the updated C3/NOx sub-mechanism, reproduces the sensitisation effect of NOx on C3H8 with generally good agreement. Sensitivity and flux analyses have been performed to highlight the key reactions controlling ignition. The analyses show that competition between the reactions Ṙ+NO2↔RȮ+NO and Ṙ +NO2 (+M) ↔ RNO2 (+M) governs NOx sensitization on propane ignition. The inhibiting effect of NO and NO2 addition to propane stems from the nĊ3H7+ NO2↔ nC3H7Ȯ + NO and nC3H7Ȯ2 + NO ↔ nC3H7Ȯ + NO2 reactions, which compete for nC3H7Ȯ2 radicals, reducing the rate of isomerization of nC3H7Ȯ2 into Ċ3H6OOH1–3 (RȮ2 ⇌ Q˙OOH).

Reactivity and Loss Mechanisms of NO3 and N2O5 at a Rural Site on the North China Plain

NO3, NO2, O3, and relevant parameters were measured at a rural site on the North China Plain during June 2014. During the campaign, the average concentrations of NO3 and N2O5 were 4.8 ± 3.3 pptv and 30.5 ± 35.4 pptv, respectively. The average NO3 production rate was 1.03 ± 0.48 ppbvh−1, and the steady-state lifetimes of NO3 and N2O5 were 26 s and 162 s, respectively, indicating that the NOx chemistry in the rural site during summer was active. The uptake coefficient range of N2O5 was 0.023 to 0.118, with an average value of 0.062 ± 0.035. Meanwhile, the fitting for kNO3 was 0.013 ± 0.016 s−1, corresponding to the shorter NO3 lifetime below 1 min. The results show that the indirect loss pathways caused by the heterogonous uptake of N2O5 contributed 64–90% of the overall NO3 loss, with an average of 81%, suggesting that the N2O5 heterogeneous reaction dominated the nocturnal NOx loss over this region.

The NH[formula omitted]/NO[formula omitted]/O[formula omitted] system: Constraining key steps in ammonia ignition and N[formula omitted]O formation

Amine/NO2 interactions are important for ignition and N2O emissions in ammonia combustion. In the present work, reported results from batch reactors (580–690 K) and flow reactors (850–1350 K) for the NH3/NO2 system were re-interpreted in terms of the present understanding of the amine chemistry. Furthermore, additional flow reactor results on the impact of O2 on the NH3/NO2 reaction were presented and analyzed. Based on the experimental results and the modeling analysis, it was possible to constrain the rate constants for reactions of NH3 and NH2 with NO2 and for subsequent steps involving H2NO and HNO intermediates. The key reaction is NH2 + NO2, forming H2NO + NO (R2) and N2O + H2O (R3). The results indicate that the yield of N2O in the NH2 + NO2 reaction decreases with temperature in the 850–1350 K range, in agreement with the theoretical study by Klippenstein and coworkers. The fate of H2NO and HNO is important for the overall reactivity. In the absence of O2, formation of chain carriers is controlled by the sequence H2NO + NO2→ HNO + HONO, HNO + NO2→ NO + HONO, HONO (+M) → NO + OH (+M). At higher temperatures, in the presence of O2, the sequence H2NO + O2→ HNO + HO2, HNO + O2→ NO + HO2, NO + HO2→ NO2 + OH enhances radical formation and recycles NO2. The satisfactory agreement between experiments and modeling predictions, both without and with O2, supports the present rate constants for the reactions of H2NO and HNO with NO2 and O2, respectively.

A Model Assessment of the Occurrence and Reactivity of the Nitrating/Nitrosating Agent Nitrogen Dioxide (•NO2) in Sunlit Natural Waters.

Nitrogen dioxide (•NO2) is produced in sunlit natural surface waters by the direct photolysis of nitrate, together with •OH, and upon the oxidation of nitrite by •OH itself. •NO2 is mainly scavenged by dissolved organic matter, and here, it is shown that •NO2 levels in sunlit surface waters are enhanced by high concentrations of nitrate and nitrite, and depressed by high values of the dissolved organic carbon. The dimer of nitrogen dioxide (N2O4) is also formed in the pathway of •NO2 hydrolysis, but with a very low concentration, i.e., several orders of magnitude below •NO2, and even below •OH. Therefore, at most, N2O4 would only be involved in the transformation (nitration/nitrosation) of electron-poor compounds, which would not react with •NO2. Although it is known that nitrite oxidation by CO3•− in high-alkalinity surface waters gives a minor-to-negligible contribution to •NO2 formation, it is shown here that NO2− oxidation by Br2•− can be a significant source of •NO2 in saline waters (saltwater, brackish waters, seawater, and brines), which offsets the scavenging of •OH by bromide. As an example, the anti-oxidant tripeptide glutathione undergoes nitrosation by •NO2 preferentially in saltwater, thanks to the inhibition of the degradation of glutathione itself by •OH, which is scavenged by bromide in saltwater. The enhancement of •NO2 reactions in saltwater could explain the literature findings, that several phenolic nitroderivatives are formed in shallow (i.e., thoroughly sunlit) and brackish lagoons in the Rhône river delta (S. France), and that the laboratory irradiation of phenol-spiked seawater yields nitrophenols in a significant amount.

Dramatic changes in aerosol composition during the 2016–2020 heating seasons in Beijing–Tianjin–Hebei region and its surrounding areas: The role of primary pollutants and secondary aerosol formation

With the implementation of a series of air pollution mitigation strategies during the past decade, great air quality improvements have been observed in the BTH region. Despite of significant decreases in gaseous pollutants, such as SO2 and NO2, the enhancement of secondary aerosol formation was observed. NO3− has surpassed SO42− and OM to become the dominant PM2.5 component. We find that the reduction of POC mainly dominated the decreasing trend of OC. As for secondary inorganic components, the key processes or factors controlling the spatial-temporal variation characteristics were different. The areas with large SO42− concentrations corresponded well to those with high SO2 concentrations, while the synchronized NO3− better followed spatial patterns in O3 than NO2. From 2016 to 2020, the response of SO42− to SO2 was close to a linear function, while the reaction of NO3− to the decrease of NO2 displayed nonlinear behavior. Such different relationships indicated that SO42− was predominantly controlled by SO2, while NO3− was not only related to NO2 but also determined by the secondary conversion process. The ratios of SO42−, NO3−, NH4+, and OC to EC between 2016 and 2020 were generally higher than 1 in typical BTH cities, and the ratio of NO3− to EC was exceptionally high, with a range reaching up to 200 %. Besides, this ratio coincided well with the enhancement of Ox, indicating the potential role of Ox to secondary NO3− formation. The diurnal cycle of NO3−, O3, and NO2 concentration change rate indicated that the relative increase of O3 during nighttime may offset the effectiveness of NOX emission reduction. This study provided observational evidence of enhanced secondary NO3− formation with the rising trend of atmospheric oxidation and emphasized the importance of nighttime chemistry for NO3− formation in the BTH region.

Heterogeneous reaction of NO2 with feldspar, three clay minerals and Arizona Test Dust

Heterogeneous reaction of NO2 with mineral dust aerosol may play important roles in troposphere chemistry, and has been investigated by a number of laboratory studies. However, the influence of mineralogy on this reaction has not been well understood, and its impact on aerosol hygroscopicity is not yet clear. This work investigated heterogeneous reactions of NO2 (∼10 ppmv) with K-feldspar, illite, kaolinite, montmorillonite and Arizona Test Dust (ATD) at room temperature as a function of relative humidity (<1% to 80%) and reaction time (up to 24 hr). Heterogeneous reactivity towards NO2 was low for illite, kaolinite, montmorillonite and ATD, and uptake coefficients of NO2, γ(NO2), were determined to be around or smaller than 1×10−8; K-feldspar exhibited higher reactivity towards NO2, and CaCO3 is most reactive among the nine mineral dust samples considered in this and previous work. After heterogeneous reaction with NO2 for 24 hr, increase in hygroscopicity was nearly insignificant for illite, kaolinite and montmorillonite, and small but significant for K-feldspar; in addition, large increase in hygroscopicity was observed for ATD, although the increase in hygroscopicity was still smaller than CaCO3.

Evolution of N2O production at lean combustion condition in NH3/H2/air premixed swirling flames

In the development of ammonia - hydrogen blends as potential substitutes for fossil fuels, the retrofitting of existing devices running at very lean condition is one of the promising solutions for decarbonisation of the power sector. However, little is known about the impact of these conditions on the production of NOX, particularly N2O that is a potent greenhouse gas. Therefore, the influence of varying thermal power and Reynolds numbers on the flame and emission characteristics, especially N2O, of ammonia-hydrogen-air swirling flames has been evaluated for the first time through the use of spatially resolved OH*, NH* and NH2* chemiluminescence, spectrometry analyses and advanced emissions characterisation at a fixed lean equivalence ratio, Φ = 0.65, representative of the Dry Low NOX (DLN) approach in traditional stationary gas turbines. NO and NO2 emissions were found to be decreasing (from ∼ 5000 ppmv to ∼ 1000 ppmv; NO and from ∼ 150 ppmv to ∼ 50 ppmv; NO2) with increasing ammonia content (from 50% to 90%) in the fuel while N2O followed reverse trends (from ∼ 50 ppmv to ∼ 200 ppmv). More than 80% ammonia content in the fuel blends exhibited high amounts of unreacted ammonia fractions (∼ 100 to ∼ 1200 ppmv), which can be potentially linked to flame instability and/or low temperatures. Furthermore, any increasing or decreasing trends in NOX with ammonia fraction were made more extreme by increasing thermal power or Reynolds number due to the differences in relevant radicals (NH, OH, NH2 etc.) formation in the flames. Experimental results suggest the unviability of these blends at the conventional lean conditions utilised at the DLN power applications due to excessive NOX emissions. Detailed sensitivity analyses of N2O concentration at the flame and post flame zone has been carried out utilising Ansys Chemkin-PRO to identify and investigate the reactions responsible for N2O formation/consumption in the experimental flames. Results have identified the reaction NH + NO ↔ N2O + H as the major source of N2O production in the flame, while the reactions N2O + H ↔ N2 + OH and N2O(+M) ↔ N2 + O(+M) are responsible for N2O consumption at the post flame zone, with higher reactivity for the latter reaction at longer residence time and relatively lower temperatures.